Physical interaction.
WHAT SIZE TARGETS NEED TO BE
Large enough to tap reliably without looking carefully.
WHY
A finger is imprecise, and the finger obscures the target.
WHAT SPACING THEY NEED
Enough that a near miss does not hit something else.
WHAT TO BE PARTICULARLY CAREFUL WITH
Destructive actions adjacent to common ones Small links within text Controls at the very edge of the screen
WHERE THE THUMB REACHES EASILY
The lower and middle portion of the screen.
WHAT THAT MEANS
Primary actions low and central are easier than top corners.
WHAT TO AVOID
Important controls in the top corners of a large phone Controls requiring two hands
WHAT TO CONSIDER
That many people hold a phone one-handed while doing something else.
WHAT ELSE MATTERS
Feedback on touch, so a tap is confirmed.
WHAT TO TEST
Using the interface one-handed, walking.
WHAT THAT REVEALS
Every target too small and every control out of reach.
